Dielectric wave guide closure



Dec. 4, 1951 A ROSENCRANS 2,577,158

DIELECTRIC WAVE GUIDE CLOSURE Filed May l3, 1948 NVENTQ CHARLES A. ROSENCRANS ORNEY Patented Dec. 4, 1951 NITED STATES DIELECTRIC WAVE GUIDE CLOSURE Application May 13, 1948, Serial No. 26,772

'7 Claims.

This application refers to waveguides, and more particularly to means for mechanically closing an open or radiating portion of a waveguide with a dielectric closure.

It is often desirable to utilize a waveguide having an open end or mouth from which electromagnetic radiation is propagated after passage through the guide. Frequently the radiation is transmitted into open space and it is often further desirable that the waveguide portion from which the radiation is transmitted be located in the open air where it is susceptible to the deteriorating influence of the weather. Furthermore, if the waveguide is to handle large amounts of power, it is frequently desirable that it be pressurized, that is, that the interior of the waveguide be filled with certain gases above atmospheric pressure, whereby the moisture of the gas within the waveguide is controlled and is kept.

below a value at which the waveguide might spark due to the large amounts of power being carried through it. Sometimes it is desired that the waveguide be evacuated for the same reason that one is pressurized, namely,'to keep the performance of the guide independent of ambient weather conditions and to protect the interior of the guide, which may be coated with a precious metal, from the deteriorating effects of the atmosphere. There is presented, simultaneously with the problem of mechanically closing the guide, the problem of electrically matchin the waveguide proper and open space or the space into which the open portion of the waveguide radiates. It is necessary, of course, that the mechanical closure for the waveguide permits the guide to remain open insofar as electromagnetic radiation is concerned, that is, that the closure be mechanically effective and microwave transmissive. Accordingly, it has been the practice heretofore to close the end of the waveguide with a window of mica or the like which is transparent to electromagnetic radiation and to accomplish matching by metal windows or the like placed in the guide at proper points therein, so that the impedance of the waveguide is matched to the impedance of outer space or the space into which the guide radiates, for the particular opening and guide being used. 7

It is an object of the present invention to pro vide a mechanical closure for a waveguide which 7' is transmissive to electromagnetic radiation and guide,

tween space within and spaceoutside the wave-.-

- broad walls, as is well known in the art,

It is a further object of the invention to provide such a closure which is broad band in effect, that is, which'matches the waveguide and the space into which it opens over a comparatively large band of frequencies.

It is a still further object of the invention to provide such a closure which gives a more effective impedance matching effect than has been heretofore possible.

It is a further object to provide such a closure.

for a rectangular guide which matches the guide to open space.

In accordance with the invention, I provide a closure made of dielectric material which is preferably characterized by comparatively low high better mechanical closure for the guide which is more sturdy and more reliable than the closures previously employed.

Other objects, advantages, and novel features of the invention will be apparent from the fol-' lowing description and the accompanying drawing, in which:

Figure 1 is a perspective view of a closure element of the invention; and

Figure 2 is a plan view of the closure in the waveguide, the latter being shown partly in sec tion for clarity.

Referring now to Figures 1 and 2 of the draw-1 ing, in which like parts bear like reference numerals, a rectangular waveguide ID has broad parallel walls I2 and M and narrow parallel walls 16 and I8. conventional manner to transmit energy over a certain band of frequencies in the T. Em mode with the electric vectors perpendicular to the The open end or mouth 20 of the waveguide has the broad walls I2, M extending somewhat farther from the waveguide than the narrow walls l6, l8, which are terminated in advance of the terinina tion of the broad walls 12 and M. Thus portion 22, of the broad wall M, is brought beyond the termination of the narrow walls I5, l8 by beveled portions '2 l 24', and then terminated in a common plane with that of broad wall It (which is similarly extended beyond the termination of narrowiwalls I6, l8) transverse to the waveguide The waveguide is proportioned in axis. The closure member 30 is inserted in the waveguide, a short distance from the mouth 28, and has a portion 3! rectangular in a cross-section normal to the axis. Portion 3| has planar surfaces 32, 34 which are fitted respectively against the internal surfaces of the board walls 12 and IA. The portion 3| has planar side surfaces 36, 38 which are fitted against the internal surfaces of the narrow walls 15, I8. On the side of portion 3| away from mouth 28 the block 30 has a tapered portion 49 which is smoothly tapered with the axis of the waveguide and with no diminution of the dimension between the surfaces 36, 38. The tapered portion 45 terminates in what might be characterized as a knife edge 42 having a notch 45 centrally located thereof. On the side of portion 31 facing the opening or mouth 29, block 36 has beveled edges 46, 48 which are perpendicular to the broad walls I2, 14 and terminate at rectangular surface 50 which extends completely between the broad walls l2, M. but does not extend completely between the side walls It, I8. I find that best results are obtained if the over-all axial length of block 36 exceeds several wave lengths, and if the distance from face 50 to the plane in which walls 22, 24 terminate is about one-eighth free space wave length, at the center frequency of the desired operating frequency.

In operation it is found that a matching impedance is obtained by a certain length of the tapered portion 10 and also bythe size and depth of the notch 54 as well as by the beveled edges 46, 48. I have found that the notch i -l permits fine adjustment of the matching efiect, so that standing Waves in the guide may be brought to minimum. The block 33 is preferably formed of a low loss dielectric material, for example, polystyrene and is readily fabricated of one piece and may be easily inserted through the open endor mouth 2!] of the waveguide and sealed therein a short distance from the mouth. If a hermetical seal is not required or desired, for example, as in scme pressurized waveguides where small gas escapage is permitted or desired, a press-fit or tight fit may be sufiicient without a sealing fit. It will be understood, of course, that the distance from the mouth 26 also affects the match to be made, as well as the dielectric constant of block 39. I have found that the closure block 38 provides a broad band match whicn is much better and broader than those matching devices heretofore used, and which gives a much better control over the closeness of the matching. It will be understood, of course, that the waveguide is equally well matched for reception purposes from outer space as for the purpose of transmission by electromagnetic energy into the outer space from the mouth 20.

The following explanation of the efiect of the closure herein described is probably the correct oneyin so far as I currently have had an opportunity to investigate the action of the closure. The tapered edge of the closure provides a gradual transition from the interior of the waveguide to the dielectric filled portion ,thereof. This gradual transition is aided by the fact that the energy propagated in the guide, assuming that the energy is traveling from the interior of theguide to the exterior, first meets the transition element'at portions where the electric field vectors are smaller in-amplitude, that is, near the narrow walls of the rectangular guide in-this instance. Thus, in a manner of speaking, the dielectric appears to the advancing electrical energy as :a. smooth transition.

Moreover, be-

cause the length of the tapered portion is several wave-lengths it is believed that the broad-band ing result is better than an abrupt transition. On the other side of the guide, there is necessarily an abrupt transition from the waveguide itself to the outer space, and this is matched by the suitable beveling of the edges of the dielectric element. This beveling is in. the described embodiment, identicalwith the beveling of the broad. walls at their termination. I have found that the most critical feature in obtaining a good impedance match'is the spacing from the mouth,

which probably varies somewhat with the dielectric constant of the dielectric material used.

Furthermore, the notch aids the broad-banding effect because, qualitatively speaking, the energy enters the dielectric medium in a manner which is notlinear with distance from the tapered edge along the axis of the guide, but at a rate which increases with distance from the tapered edge along the taper, to a greater degree than without the notch. With this closure element the guide can be matched to outer space with a selected opening, and it is not necessary to use the horn type openings to radiate to outer space. The latter openings have the disadvantage of restricting the radiation pattern to certain types or" patterns which it is sometimes desired to avoid. Speaking still qualitatively and in a general way, the tapered notched portion matches the waveguide proper, and the beveled portion matches the beveled opening.

Not by way of limitation, but in order to enable those skilled in the art 'to duplicate the results I have obtained with a preferred embodiment and to build and use a closure of the new and improved type disclosed herein, the drawing shows the dimensions of the closure element in inches.

Its spacing from the waveguide mouth and the dimensions of the guide mouth utilized will be apparent from the drawing. The operating'frequency in the embodiment illustrated was about 7000 megacycles per second.

What is claimed is:

l. The combination of a waveguide having sidewalls and having an opening for the transfer of electromagnetic energy between the space within said waveguide and space outside the waveguide, and a closure and energy transfer matching element for said Waveguide positioned entirely 'therewithin and having a first portion provided with sides fitted to said waveguide sidewalls, said element being of solid dielectric material and having an end portion closer to and an end portion .moreremote from said opening than said first portion, each of'said end portions being progressively smaller in cross-se'ctionwith axial distance from said first portion and said end portion more remote from said waveguide opening being axially longer than said 'end portion closer to said opening, said end portionmore remote from said waveguide opening being tapered 'to'a knife edge, said end'portion closer to said waveguide opening having bevelededges.

2. The combination'of-a rectangular waveguide having a first pair 7 of walls parallel to each other and a second pair of walls parallel'to each other. and normal to said first pair'of walls 'for the transmission of electromagnetic energy within said "waveguide with the electric vector normal to said first pair of walls, said second pair being separated by a distance "affording transmission in the TE0,1 mode at the operating frequency, and having an open :mouth for'the transfer of electromagnetic energy between the space within said waveguide and space outside the waveguide, and a closure and energy transfer matching element for said waveguide positioned entirely therewithin and having a first portion provided with sides fitted to said waveguide sidewalls, said element being of solid dielectric material and having an end portion closer to and an end portion more remote from said opening than said first portion, each of said end portions being progressively smaller transversely with axial distance from said first portion, said end portion more remote from said waveguide mouth being tapered with dimensions thereof parallel to said second pair of waveguide walls progressively diminishing with axial distance from said mouth, the other said end portion closer to said waveguide mouth having beveled edges, the beveled surfaces of said beveled edges being substantially perpendicular tosaid first pair of waveguide walls. a

3. The combination claimed in claim 2, said tapered portion being tapered to a knifeedge substantially parallel to said first pair of walls.

4. The combination of a rectangular waveguide having a first pair of walls parallel to each other and a second pair of walls parallel to each other and normal to said first pair of walls for the transmission of electromagnetic energy within said waveguide with the electric vector normalto said first pair of walls, said second pair being separated by a distance to afford transmission in the 'IEo,1 mode, at the operating frequency, and having an open mouth for the transfer of electromagnetic energy between the space within said waveguide and space outside the waveguide, and a closure and energy trans- I fer matching element for said waveguide positioned entirely therewithin and having a first portion provided with sides fitted to said waveguide sidewalls, said element being of solid dielectric material and having an end portion closer to and an end portion more remote from said opening than saidfirst portion, each of said end portions being progressively smaller transversely with axial distance from said first portion, said end portion more remote from said waveguide mouth being tapered with dimensions thereof parallel to said second pair of waveguide walls progressively diminishing with axial distance from said mouth, the other said end portion closer to said waveguide mouth having beveled edges, the beveled surfaces of said beveled edges being substantially perpendicular to said first pair of waveguide walls, said tapered end portion being tapered to a knife edge substantially parallel to said first pair of walls, said knife edge being centrally located between said first pair of walls in said waveguide.

5. The combination claimed in claim 4, said knife edge having a notch centrally thereof.

5. A combination closure and'energytransfer matching element for insertion entirely within a rectangular waveguide having an open mouth for the transfer of electromagnetic energy between the space within said waveguide and the space outside said waveguide, said element being of solid dielectric material and having a first portion provided with sides which fit the waveguide sidewalls on insertion therewithin to mechanicaily close the waveguide, and having end portions which, upon insertion, are axially closer to and more remote from said opening than said first portion, each of said end portions being progressively smaller transversely with axial distance from said first portion, said more remote portion being tapered to a knife edge, said knife edge having a notch centrally thereof.

7. A combination closure and energy transfer matching element for insertion in a waveguide having an opening for the transfer of electromagnetic energy between the space within said waveguide and space outside the waveguide, said element being of solid dielectric material and having a first portion provided with sides which REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,413,187 McCurdy et al. Dec. 24, 1946 2,427,098 Keizer Sept. 9, 1947 2,453,414 De Vore Nov. 9, 1948 2,454,530 Tiley N0v.'23, 1948 2,460,401 Southworth Feb. 1, 1949 FOREIGN PATENTS Number Country Date 590,651 Great Britain July 24, 1947 

